# Copyright 2018 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS-IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""A memoization decorator."""


def memoize(func):
  """Memoization decorator."""

  class Memodict(dict):
    """A memoization decorator dict."""
    __slots__ = ()
    __name__ = func.__name__
    __doc__ = func.__doc__

    def __call__(self, *args):
      return self[args]

    def __missing__(self, args):
      ret = self[args] = func(*args)
      return ret

  return Memodict()
